1. Field of the Invention
The present invention relates in general to the field of information handling system cable interfaces, and more particularly to a system and method for monitoring information handling system interfaces through cables having plural links.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems often interact with each other and with peripheral devices through external cables. In some instances, information handling system external cables have plural links with each link supporting a communication interface. As an example, in external Serial Attached SCSI (SAS) environments, a cable having four links defined by the SAS standard interfaces devices connected by the cable with a width of one, two, three or all four links. For instance, SAS devices, such as storage devices, interfaced with an SAS external cable typically communicate through all four links. Other SAS devices, such as switches and concentrators used in storage networks accept SAS cables but only interact through two of the four links on the cable. Some SAS devices, such as tape drives, accept SAS cables but only interact through one of the four links. The number of links used by a particular device depends upon the SAS controller card used in the device. For some devices, using all links available through a cable connection adds cost without substantial improvement in the speed at which information is communicated.
Devices interfaced though a cable generally include internal logic to monitor the quality of the cable connection and sometimes include external indicators of the cable connection quality, such as LED lights. For example, SAS controllers establish communication over a link by achieving DWord synchronization and then exchanging an IDENTIFY address frame. With a standard SAS controller, detection of a DWord synchronization at each link of a cable port is sometimes used to illuminate an LED to indicate normal operations. If one or more links of a cable port does not have DWord synchronization, the LED is illuminated amber instead of green to indicate a potential problem or degraded operations. If none of the links of a cable port has DWord synchronization, the LED is not illuminated to indicate a failure of normal operations. In addition to visual indications of an SAS controller's operational status, a device associated with the controller often monitors DWord synchronization status to determine difficulties in operations.
Difficulty tracking proper operation of devices sometimes arises when devices are interfaced by a cable having plural links, such as an SAS cable, in which not all links are used. For example, an SAS cable having four links that interfaces on one end with an information handling system and another end with a tape drive might only use one link to communicate information. Although the tape drive will view a single link with DWord synchronization as indicating normal operations, the information handling system SAS controller will view a single link with DWord synchronization as indicating a potential problem with communication through the cable. If the information handling system SAS controller illuminates an amber LED, an end user has an incorrect indication of degraded operations. One way to address this problem is to have specialized controllers for devices that use less than all links of a cable. However, manufacturing and tracking specialized controllers adds expense and complexity to system operations.